In general, the process for manufacturing a semiconductor wafer comprises the steps of obtaining wafers by cutting and slicing out of a single crystal ingot, and chamfering the respective wafers, mechanical grinding (lapping), etching, mirror-polishing, and cleaning, thereby producing a wafer with highly precise flatness. The wafer, which has been subjected to the steps for mechanical processing, such as block-cutting, rounding, slicing, and lapping, has a damaged layer (i.e., a processing-strained layer) on the surface thereof. In the process for device production, such a processing-strained layer causes crystal defects, such as slip dislocation, and the mechanical strength of the wafer is then decreased. In addition, it has adverse effects on electric characteristics. Therefore, the processing-strained layer should be completely removed. For removing such a processing-strained layer, an etching process is carried out. There are two types of etching: dip-etching and single wafer etching.
Among the etching processes, the single wafer etching has been regarded as the most suitable etching process, which enables the control of the texture-size and surface roughness of a large-sized wafer. The single wafer etching is a process comprising dropping an etching solution onto the front surface of a flattened single wafer and horizontally rotating (spinning) the wafer to spread out the dripped etching solution over the front surface of the wafer. The etching solution supplied on the wafer is spread out over the surface of the wafer from a supplied point by centrifugal force caused by horizontally spinning the wafer, and finally reaches the edge of the wafer, so that the edge of the wafer as well as the front surface thereof can be also etched at the same time. Furthermore, most of the etching solution supplied is blown off from the edge thereof by centrifugal force and then collected into a cup or the like arranged on an etching device.
For example, as a process for manufacturing a semiconductor wafer that can effectively remove a processing-strained layer caused by mechanical grinding and retain the flatness of the wafer, there is disclosed one including the following steps; slicing a silicon single crystal ingot; chamfering the end face of the sliced wafer; flattening at least the front surface thereof obtained by slicing the semiconductor ingot by means of surface grinding or lapping; spin-etching the flattened front surface of the wafer; and polishing the etched front surface of the wafer into a mirror surface (e.g., see Patent Document 1).
Patent Document 1
Japanese Unexamined Patent Application Publication No. 11-135464 (claim 1, FIG. 1)